This invention relates generally to an electrophotographic printing machine, and more particularly concerns a sheet feeding and leveling apparatus which allows a copier or printer to feed and/or stack forms whose thickness varies from end to end.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
In a high speed commercial printing machine of the foregoing type, large volumes of copy sheets are fed from storage to the transfer station of the printing machine where the toner powder image is transferred to the copy sheet. Frequently, the copy sheets are stored on a elevator type of sheet feeding tray. The tray is mounted on a frame and moves vertically from a sheet loading to a sheet feeding position. High capacity printing machines require large amounts of copy sheets. For example, a fully loaded tray may be loaded with several reams of paper with each ream containing approximately five hundred sheets. The sheet feeder advances successive uppermost copy sheets from the stack of copy sheets mounted on the tray. Frequently, specialized forms are developed for certain customers in response to unique requirements. Such specialized forms consist of preprinted paper sheet and include labels affixed to one portion of each sheet. In the area of the label (and its associated release paper), the sheet is thicker than elsewhere, causing there to be a "stack build up" where the sheets are stacked one on top of the other as shown schematically in FIGS. 6 and 7. Sheet feeding and stacking mechanisms typically require the top of the stack to be horizontal for reliable feeding. Therefore, the stack build up condition limits the capacity of the machine to small stacks for reliable feeding. The copy sheets are loaded on the tray with the thicker end usually being the trail edge of the stack of copy sheets resulting in the trail edge of the stack of copy sheets being thicker than the leading edge of the stack of copy sheets. Under these circumstances, the leading edge of the stack of copy sheets is lower than the trailing edge thereof. This out of level condition results in significant sheet feeding problems, such as sheet stubbing, misfeeding and multifeeding.
Various approaches have been devised for leveling sheets. The following disclosures appear to be pertinent:
U.S. Pat. No. 2,471,066 PA1 Patentee: Hesson PA1 Issued: May 24, 1949 PA1 U.S. Pat. No. 2,886,314 PA1 Patentee: Phelan PA1 Issued May 12, 1959 PA1 U.S. Pat. No. 4,593,895 PA1 Patentee: Myers et al. PA1 Issued: Jun. 10, 1986 PA1 U.S. Pat. No. 4,942,435 PA1 Patentee: Kneisel et al. PA1 Issued: Jul. 17, 1990
The relevant portions of the foregoing patents may be summarized as follows:
U.S. Pat. No. 2,471,066 discloses a compensator mechanism for uneven thickness sheet feeding for use on a can labeler. A hinged section moves up or down to maintain the top of the stack level.
U.S. Pat. No. 2,886,314 describes a compensator mechanism for uneven thicknesses of paper. The mechanism uses a pair of compensator bars for raising the middle as well as one end of the stack to level the top.
U.S. Pat. No. 4,593,895 discloses a cash dispensing machine cassette having a stack of bills with their long lower edges supported on a floor when loaded in the cassette. A pair of resilient pushers engage the rear of the stack of bills to slide the bills into operative engagement with an ATM which discharges bills therefrom.
U.S. Pat. No. 4,942,435 discloses a leveling supporting means for use in an electrostatographic machine for supporting a stack of sheets that is adapted to be interposed between a tray and a stack of copy sheets when one marginal region of the stack has a greater thickness than the other marginal region. The supporting means includes means for fixedly supporting the other marginal region of the stack of sheets and means for resiliently supporting at least the one marginal region of the stack of sheets having the greater thickness.
In accordance with one aspect of the present invention, there is provided an removable, modular apparatus adapted to be removably mounted on an elevator mechanism for supporting a stack of sheets wherein one marginal region of the stack has a greater thickness than the other marginal region of the stack. The apparatus includes means for fixedly supporting the other marginal region of the stack of sheets in a substantially horizontal plane. Means are provided for resiliently supporting at least the marginal region of the stack of sheets having the greater thickness such such that the majority of the sheets that include the greater thickness extend at an acute angle with respect to the horizontal plane. The fixedly supporting means and the resilient supporting means engage the lowermost sheet of the stack to support the stack of sheets so that at least the opposed marginal regions of the uppermost sheet of the stack are at substantially about the same level.
Pursuant to another aspect of the features of the present invention, there is provided an electrophotographic printing machine of the type having a latent image developed on a photoconductive member and in which the developed image is transferred to a copy sheet with successive copy sheets being supplied from a supply source thereof. The printing machine includes an elevator adapted to receive a tray placed thereon that is arranged to have a stack of copy sheets disposed a surface thereof. The tray is adapted to be placed upon the elevator when one marginal region of the stack of copy sheets has a greater thickness than the other marginal region thereof, and supports the stack of copy sheets so that at least opposed marginal regions of the uppermost sheet of the stack of copy sheets are at substantially about the same level while the majority of those portions of the copy sheets having the greater thickness extend at an acute angle with respect to the plane of the uppermost sheet of the stack.